Xerographic cleaning apparatus

ABSTRACT

Method and apparatus for cleaning residual toner material from a photoconductive surface in automatic xerographic processing apparatus in which the photoconductive surface is developed and cleaned simultaneously at a single processing station. A brush mounted at the entrance to the development-cleaning station which is vibrated to uniformly distribute residual toner over the entire area of the photoconductive surface to effect efficient cleaning.

United States Patent Inventor William C. Emerson Rochester, N.Y.

Appl. No. 796,960

Filed Feb. 6, 1969 Patented Nov. 2, 1971 Assignee Xerox Corporation Rochester, N .Y.

XEROGRAPHIC CLEANING APPARATUS 3 Claims, 3 Drawing Figs.

U.S. Cl 355/15, 96/l.4,117/l7.5,117/19,118/637, 15/1.5 1nt.C1 ..G03g 15/08, 603g 15/22 Field ofSearch 117/17.5,

l9;96/1.4; 355/15, 17; 118/637; l5/l.5

[56] References Cited UNlTED STATES PATENTS 2,756,676 7/1956 Steinhilper l17/17.5 X 3,448,724 6/1969 Chawda etal 117/17.5X 3,503,776 3/1970 Gundlach ll7/l7.5

Primary Examiner-William D. Martin Assistant Examiner-Edward J. Cabic AttarneysNorman E. Schrader and Melvin A. Klein ABSTRACT: Method and apparatus for cleaning residual toner material from a photoconductive surface in automatic xerographic processing apparatus in which the photoconductive surface is developed and cleaned simultaneously at a single processing station, A brush mounted at the entrance to the development-cleaning station which is vibrated to uniformly distribute residual toner over the entire area of the photoconductive surface to effect efficient cleaning.

PATENTEnuuv 2 |97| FIG. I

INVENTOR. WILLIAM C. EMERSON FIG. 3

ATTORNEY XEROGRAPHIC CLEANING APPARATUS This invention relates to xerography and, in particular, to cleaning residual toner material from a photoconductive surface in an automatic xerographic apparatus utilizing a development-cleaning system.

In the art of xerography, as originally disclosed by Carlson in U.S. Pat. No. 2,287,691, a plate, generally comprising a photoconductive insulating material placed upon a conductive backing, is charged uniformly and the plate surface then exposed to a light image of an original subject desired to be reproduced. The photoconductive coating is caused to become conductive under the influence of the light image so as to selectively dissipate the electrostatic charge found thereon to produce what is known as an electrostatic latent image. This image is then developed by means of a variety of pigmented resins which have been specifically developed for this purpose. The pigmented resin material, more commonly referred to as toner, is brought into contact with the photoconductive surface where the material is electrostatically attracted to the latent image in proportion to the charge found thereon. That is, areas of small charge concentration become areas of low toner density while areas of greater charge concentration become proportionally more dense. The developed image is then transferred to a final support material, as for example, paper, and fixed thereto to form a permanent record of the original subject.

Although a preponderance of the toner material making up the image is transferred to the final support material during the transfer process, some toner particles which are held to the photoconductive surface by relatively high electrostatic and/or mechanical forces remain on the surface after the transfer operation. In automatic xerographic reproducing apparatus, the residual toner must be cleaned from the photoconductive surface before the surface is xerographically reprocessed.

The size of the average toner particle employed in automatic xerography is generally about ten microns. Because of its extremely small size and fine composition, the cleaning and handling of residual toner material has long presented a special problem in automatic xerography. Many xerographic cleaning devices are known in the art, however, all of these devices suffer from the same defects in that they are space consuming.

Because of recent advances in the xerographic art it is now possible to eliminate relatively large and complex cleaning stations in automatic xerographic devices. It has been found that under certain conditions a photoconductive surface can be both cleaned and developed simultaneously by use of a conventional two component developing material in a single development-cleaning system. This novel development-cleam ing process is described in greater detail in copending application Ser. No. 789,031, filed in the name of Volkers and Cade. The Volkers apparatus-cleaning system has been found to extend the useable life of a photoconductive surface by eliminating the need for relatively harsh mechanical cleaning devices and further, because residual toner material is recovered within the developer housing, the toner recovery is almost 100 percent toner efficiency. However, as noted, in the heretofore-mentioned Volkers disclosure, maximum cleaning occurs in a development-cleaning system when the fiow of developer is the greatest as, for example, in a cascade development system. The system therefore does not readily lead itself to use in systems having a relatively low volume rate of developer flow.

It is therefore an object of this invention to improve xerography.

A further object of this invention is to improve development-cleaning apparatus wherein said apparatus can be efficiently utilized in conjunction with a gentle flow developing system.

The foregoing objects and other features of the invention may be more readily understood by reference to the following description of an exemplary embodiment of this invention to be read with reference to the drawings in which:

FIG. I is a schematic diagram showing the present invention I embodied in an automatic xerographic machine;

FIG. 2 is a graphic representation showing the relationship of background voltage to image voltage on the photoconductive surface of an automatic xerographic device as illustrated in FIG. 1,

FIG. 3 is a partial enlarged diagrammatic view of one portion of the apparatus shown in FIG. 1 illustrating the mechanics of the electrostatic transfer operation.

The apparatus of the present invention for cleaning residual xerographic toner from a xerographic plate is shown in FIG. 1. Although it will become apparent that the instant invention is well adapted for use in most xerographic reproduction apparatus, it is shown herein embodied in a drum-type xerographic machine for purposes of illustration. As shown in FIG. 1, drum 10 is mounted on shaft 11 and the shaft rotatably mounted in the machine frame (not shown). The major xerographic processing components are mounted around the drum periphery so that they are able to act thereon as the drum continually rotates through the various stations.

In general, the several xerographic processing stations in the path of movement of the drum surface may be described functionally as follows:

a charging station A, at which a uniform electrostatic charge is deposited on the surface of the photoconductive drum;

an exposure station E, at which a light or radiation pattern of a copy to reproduced is projected onto the xerographic drum to dissipate the charge in the exposed areas thereby forming a latent electrostatic image thereon;

a developing station C, at which the xerographic developing material comprising toner particles having an electrostatic charge opposite to that of the electrostatic image are placed in contact with the moving drum surface whereby the toner particles are caused to adhere to the electrostatic latent image found thereon; and

a transfer station D where the developed latent image is electrostatically transferred from the plate surface to a final insulating support material.

It is believed that the foregoing description is sufficient for the purposes of this application to show the general operation of the xerographic reproduction apparatus.

In general, the electrostatic charging of the xerographic drum in preparation to the exposure step is accomplished by means of a corona-generating device 12 whereby a positive electrostatic charge in the order of 500 to l,000 volts is applied uniformly to the drum surface. Although any number of types of corona generating devices are available, a device of the type disclosed by Vyverberg in U.S. Pat. No. 2,836,725 is used in this preferred embodiment. The corona charging device or, as herein referred to, corotron, is securely affixed to the machine frame and operatively connected to any suitable electrical source (not shown). As the drum rotates in the direction indicated, the photoconductive surface passing under corotron12 is uniformly charged. The charge surface is then moved to the exposure station where a flowing light image of an original subject to be reproduced is used to discharge the photosensitive drum in the nonimaged areas thus creating a latent image capable of being xerographically processed as described above.

Subsequent to the exposure step, the latent image is brought into contact with a two-component developer material contained within a clam shell shaped housing 13. The housing contains a sufficient quantity of developer material so that the moving drum surface will be maintained in contact with the developer material as it moves through the housing. The mechanical action of the drum against the granular developing material causes a thin layer of developer material adjacent the drum surface to move upwardly at drum speed. This thin layer of material moves in an uphill direction while the back layer of developer material in the housing moves down more or less as a unit to fill the void left by the upwardly moving material. The circular flow of developer material thus established is depicted by the arrows in FIG. 1. Theoretically, the flow established within the housing delivers properly loaded and charged developer material from the supply of developer material on the backside of the system to the start of the developer zone. The developer material introduced into the uphill flow zone is carried along in contact with the drum surface at approximately drum speed where development takes place by means of the classic xerographic development-scavanging mechanism. A point is finally reached where the mechanical action of the moving drum surface can no longer overcome the forces of gravity acting on the material and the developer returns once again to the backside of the system. A relatively gentle flow of developing material is thus maintained through the system. For further information concerning this type of development system, reference is had to copending application to Chawda, et al. Ser. No. 697,239, now US. Pat. No. 3,448,724.

Once developed, the image is transported on the photoconductive surface to a transfer station where it is electrostatically transferred from the surface to a final support material 30. Transfer is effected by means of a corona transfer device 16 located at or immediately after the point of contact between the final support material and the rotating drum surface. The corona transfer device is substantially the same as the corona discharge device employed at charging station A and is arranged to spray the backside of the final support material with positive ions when energized from a suitable high potential source (not shown). In theory, the highly positive electrostatic field established on the backside of the final transfer material electrostatically attracts and holds all the toner particles making up the image to the support material. Simultaneously with the transfer operation, the electrostatic field created by the corona discharged device also is effective in tacking the transfer material to the drum surface. The final support material, electrostatically tacked to the drum surface moves with,the rotating surface until removed therefrom by stripping means (not shown). The powder image is then permanently affixed thereto by means of radiant heat fusing 29 to form a permanent record of the original copied.

Although a preponderence of the toner material is transferred to the final support material, at this time some residual toner is found to remain on the drum surface after the transfer operation.

In the present invention, cleaning and development are accomplished at the same time within the xerographic development housing. At the time that the toner is being deposited in the image areas, image removal is also taking place with the net toner deposited on the plate surface being the difference between the two processes. In a development-cleaning system, as herein described, the net toner deposited in the image areas reaches an early maximum, that is, a preponderence of the development takes place near or at the start of the active development zone. The denuded or toner-starved carrier material, which has given up its toner in the early development process, therefore, acts to mechanically scrub and electrostatically attract loosely residual toner material from the background areas on the drum surface. This residual toner, residing in the exposed or nonimaged areas, having lesser electrostatic attraction to the plate than toner in the image areas is more readily scavenged by the denuded or partially denuded carrier materials. That is, the toner material attracted to the image area is held to the plate surface by a force field having components of higher magnitude than those found in the background areas. Because of this stronger bond the toner images are not seriously effected by the action of the partially denuded carrier material.

In practice, to make a development-cleaning system functional, it is necessary to reduce the quantity of residual toner on the drum surface to a point where the residual does not appear as dirt on subsequent copies. in this preferred embodiment of the instant invention, the developer material is preselected so that the interaction of the two components cause the toner to adhere to the carrier in a negatively charged state. As illustrated in FIG. 1, transfer corotron l6 sprays the back of the insulating support material 30 with positive ions so as to place the material at a potential sufficient to attract negative toner particles 17 from the plate surface to the support material. The negative residual toner which remains on the drum surface after the transfer operation is then moved beneath charging corotron 12 where it is brought under the infiuence of a highly positive field. Some of the previously negative toner assumes a positive charge at this time.

In this type of developing-cleaning system, it is possible to have both positive and negative residual toner material entering the developing-cleaning housing at the same time. The negative residual toner, that is, the toner having a charge opposite to that found on the carrier material, is readily cleaned from the drum surface because it is subjected to both a mechanical scrubbing action and an electrostatic attraction when contacted by the denuded or partially denuded carrier material. On the other hand, positive residual material, because it possesses a like charge as that found on the carrier material can only be mechanically scrubbed from the drum surface. Therefore, in a gentle flow system as herein described, only a limited amount of mechanical action is available to produce the needing scrubbing action to remove this toner from the plate surface.

It is known and has been shown experimentally that very strong electrostatic fields exist at or near the boundaries of a charged image area and the strength to the component force field rapidly drops off as you move away from the boundary or fringed areas. A typical force component distribution is shown graphically in FIG. 2. Assuming that a relatively straight perpendicular imaginary line 19 separates the charged imaged areas and the background or nonimaged areas on the photoconductive surface, we find that there exists substantially perpendicular force field components in the image force field and the strength of these components reaches a maximum very close to the line of separation.

In the xerographic process described herein, image development depends mainly upon the potential difference or electrostatic contrast found between the image and nonimaged area rather than on the total charge placed on the plate. If for ex ample, the photoconductive surface were charged uniformly over its entire surface a force field of substantially equal perpendicular force component would be created. However, even though the plate is highly charged, little or no strong force field components exist to which toner would be attracted. In other words in the absence of electrostatic contrast little or no image development can be produced. By exposing the uniformly charged plate to a light image, the uniform charge pattern is broken up thus creating the needed electrostatic contrast to develop an image. As illustrated in FIG. 2, the potential in the nonimaged areas (V,,) is not reduced to zero after exposure. However, the background potential is reduced sufficiently in relation to the image potential (V,) so that sufficient electrostatic contrast exists to effect development.

It has been found that the high electrostatic contrast in the fringe areas is not entirely dissipated during the xerographic process. A relatively weak force field usually remains on the plate surface in the fringed areas after image transfer and after plate discharge. This force field, because it is in the fringe areas, has both a positive and negative attraction and therefore is capable of attracting and holding both positive and negative residual toner. As explained above, because the carrier material in the present developer system is moving in a relative low volume rate of flow, positive toner, which is held in the residual fringe areas, cannot be electrostatically attracted to the toner and is not readily scrubbed from the drum surface by a mechanical bead action. If this positive toner is allowed to build up any fringed areas, the amount of electrostatic contrast that can be produced by the system will be eventually reduced to a level where development is impaired.

In the present invention, a vibratory brush 22 is positioned upstream from the point where the drum surface enters the development cleaning system (FIG. 1). The brush 22 is mounted longitudinally along the drum surface so that the brush fibers are in light touching contrast with the photoconductive surface thereon. A vibratory motor 21 communicates with the brush through means of flexible member 23. In operation, the brush fibers are vibrated transversely across the drum surface while in contact therewith and act to reposition or puddle the charged residual toner particles uniformly over the entire drum surface. It should be clear, brush 22 is not a cleaning brush in the xerographic sense and is functionally employed herein to puddle the charge toner material adhering to the plate surface rather than remove the toner therefrom. When the charged residual toner is lightly agitated, as for example by means of the vibratory brush herein disclosed, the toner is repositioned uniformly across the drum surface. This continual uniform repositioning of the residual toner material precludes toner from building up in the fringe areas. Furthermore, by relocating the residual toner material held in the fringe areas into areas of weaker electrostatic attraction, the partially denuded carrier material can be far more efficiently employed in the developing-cleaning housing to mechanically clean the plate surface.

While this invention has been described with reference to the structure disclosed herein, it is not confined to the details set forth and this application is intended to cover modifications and changes as may come within the scope of the following claims.

What is claimed is:

l. in an automatic xerographic reproducing device in which a photoconductive surface is moved past xerographic processing stations including a charging station, an exposure station, a development station, and a transfer station to transfer the developed image from the photoconductive surface, and the development station includes apparatus of the type wherein a flow of two-component developer is brought into contact with the moving photoconductive surface to simultaneously develop said surface and to clean charged residual toner therefrom, the improvement comprising,

a brush support with the brush fibers in light touching contact with the movfing surface and being mounted at a position wherein the brush fibers contact said surface prior to the surface being contacted by the developer material and after exposure, and

vibrating means operatively connected to said brush to vibrate said brush with an amplitude and frequency of vibration sufficient to uniformly and evenly distribute charged residual toner particles on the plate surface whereby the residual toner is efficiently removed by the flow of two-component developer material.

2. The apparatus of claim 1 wherein said movable photoconductive surface is a xerographic drum.

3. The apparatus of claim 2 wherein said brush is mounted longitudinally to the drum surface and is vibrated transverse to the direction of drum movement. 

1. In an automatic xerographic reproducing device in which a photoconductive surface is moved past xerographic processing stations including a charging station, an exposure station, a development station, and a transfer station to transfer the developed image from the photoconductive surface, and the development station includes apparatus of the type wherein a flow of two-component developer is brought into contact with the moving photoconductive surface to simultaneously develop said surface and to clean charged residual Toner therefrom, the improvement comprising, a brush support with the brush fibers in light touching contact with the moving surface and being mounted at a position wherein the brush fibers contact said surface prior to the surface being contacted by the developer material and after exposure, and vibrating means operatively connected to said brush to vibrate said brush with an amplitude and frequency of vibration sufficient to uniformly and evenly distribute charged residual toner particles on the plate surface whereby the residual toner is efficiently removed by the flow of two-component developer material.
 2. The apparatus of claim 1 wherein said movable photoconductive surface is a xerographic drum.
 3. The apparatus of claim 2 wherein said brush is mounted longitudinally to the drum surface and is vibrated transverse to the direction of drum movement. 